The present invention relates to a device for measuring the distribution and/or impulse of a series of droplets, such as a stream of monodisperse droplets dispensed from a process liquid dispenser during processing of a semiconductor wafer.
The trend toward ever smaller semiconductor device structures formed on semiconductor wafers requires continual development of the equipment used to process those wafers. Commonly-owned U.S. Pat. No. 8,691,022 describes a process liquid dispenser in a device for treating semiconductor wafers, in which the process liquid is dispensed as a series of monodisperse droplets. Such a process liquid dispenser is advantageous from the standpoint of the reproducibility of the process results, as well as a reduced incidence of undesired damage to the submicroscopic device structures formed on the semiconductor wafer undergoing processing.
It is desirable to monitor the performance of such a dispenser between processes to ensure that the dispenser is exhibiting stable performance, for example, that the stream of droplets retains its monodisperse character, and that the size and frequency of the droplet stream is within an acceptable tolerance.
Conventional techniques for monitoring a series of monodisperse droplets involve assessing the droplet stream optically, for example with a stroboscopic camera system that includes a CCD camera with a microscope lens and an associated strobe to illuminate the droplet stream. Droplets can then be visualized by triggering the stroboscope and the camera simultaneously.
However, the equipment for optical monitoring of a droplet stream is expensive, and moreover requires visual analysis of the photographic images in order to effect any adjustments to the droplet characteristics.
A simpler and more automated technique for monitoring the distribution and/or impulse of a series of droplets could facilitate the implementation of such droplet dispensers in a variety of useful applications.